CHAPTER 38
Anatomical and Physiological Characteristics of Tentacular
Nematocytes Isolated by Different Methods from Aiptasia diaphana
(Cnidaria: Anthozoa) in the Brackish Pond Faro (Messina, Italy)
G. La Spada, A. Marino, and G. Sorrenti
ABSTRACT
We studied the effects of isolation on anatomical and functional characteristics of nematocytes
isolated from tentacles of Aiptasia diaphana, an anthozoan living in the brackish pond Faro
(Messina) where salinity can change for both climatic and anthropic reasons. The anatomical
effects of isolation were investigated by scanning electron microscopy (SEM). To evaluate the
functional effects, the capacity to regulate cell volume under a 35% hyposmotic shock
(Regulatory Volume Decrease, RVD) was measured by image computer processing of the sagittal area. Furthermore the membrane integrity was revealed by applying Trypan blue. The isolation using a physical method was performed by heat dissociation (45°C for 20 min), while, as a
chemical method, we used a treatment of tissue with SCN-, The isolated nematocytes revealed
different characteristics both anatomical and physiological, although the Trypan blue test
showed that in both cases the cell membrane was not damaged. In particular nematocytes isolated by heat dissociation show the mechanosensorial apparatus while those isolated by SCNappeared to be deprived ofthis structure. As far as the volume regulation is concerned, the cells
isolated by heat dissociation did not appear to regulate their volume until the hypotonic treatment was maintained. On the other hand the nematocytes isolated by SCN- regulate volume in
hypotonic conditions.
Introduction
The nematocytes are particular stinging cells
of Cnidaria (Coelenterates), They have a
mechanosensorial apparatus which makes them
mechanoreceptive, while either support or sensorial cells, which have specific membrane receptors, act as chemoreceptors (Watson and
Hessinger 1992; Mire-Thibodeaux and Watson
1994). A particular feature of the nematocytes is
that of synthesizing the nematocyst, made up of a
wall and an inverted tubule immersed in the capsule fluid (Mariscal 1974). The application of
chemical and mechanical stimulation (Pantin
1942) results in a rapid extroflexion of the tubule
which penetrates the tissues of the target. injecting toxins of the capsule fluid (Burnett 1991;
Norton 1991; Long and Burnett 1994). This phenomenon is called discharge and it is the most
rapid process of exocytosis known today
(Holstein and Tardent 1984). It is regulated in situ
not only by nematocytes, but also by support and
sensorial cells and, as has recently been shown, a
release of nitric oxide (Salleo et al. 1996); therefore it was deemed as useful to carry out research
on isolated nematocytes in order to eliminate the
possibility of interference by other cells.
So far, either chemical methods, such as
either enzymatic (Anderson and McKay 1987;
McKay and Anderson 1988) or non-enzymatic
(Salleo et al. 1996; Barra et al. 1997), or physical,
such as maceration and heat dissociation
(Schmid et al. 1981; Weber 1995) have been
attempted to isolate nematocytes from various
species. Recently Weber (1995). on the basis of
what Schmid reported (l981). proposed a new
non fixative physical method using two labelling
dyes, in order to investigate nematocyte
turnover and inCUbating Hydra specimens at
40°C for 10 min in a hypertonic medium, obtainIstituto di Fisiologia Generale, Universita di Messina, Salita Sperone 31,98016 Messina, Italy
EM. Faranda, 1.. Guglielmo, G. Spezie (eels)
Mediterranean Ecosystems: Structures and Processes
@ Springer-Verlag ltalia 2001
Anatomical and Physiological Characteristics of Tentacular
Nematocytes Isolated by Different Methods from Aiptasia diaphana
(Cnidaria: Anthozoa) in the Brackish Pond Faro (Messina, Italy)
G. La Spada, A. Marino, and G. Sorrenti
ABSTRACT
We studied the effects of isolation on anatomical and functional characteristics of nematocytes
isolated from tentacles of Aiptasia diaphana, an anthozoan living in the brackish pond Faro
(Messina) where salinity can change for both climatic and anthropic reasons. The anatomical
effects of isolation were investigated by scanning electron microscopy (SEM). To evaluate the
functional effects, the capacity to regulate cell volume under a 35% hyposmotic shock
(Regulatory Volume Decrease, RVD) was measured by image computer processing of the sagittal area. Furthermore the membrane integrity was revealed by applying Trypan blue. The isolation using a physical method was performed by heat dissociation (45°C for 20 min), while, as a
chemical method, we used a treatment of tissue with SCN-, The isolated nematocytes revealed
different characteristics both anatomical and physiological, although the Trypan blue test
showed that in both cases the cell membrane was not damaged. In particular nematocytes isolated by heat dissociation show the mechanosensorial apparatus while those isolated by SCNappeared to be deprived ofthis structure. As far as the volume regulation is concerned, the cells
isolated by heat dissociation did not appear to regulate their volume until the hypotonic treatment was maintained. On the other hand the nematocytes isolated by SCN- regulate volume in
hypotonic conditions.
Introduction
The nematocytes are particular stinging cells
of Cnidaria (Coelenterates), They have a
mechanosensorial apparatus which makes them
mechanoreceptive, while either support or sensorial cells, which have specific membrane receptors, act as chemoreceptors (Watson and
Hessinger 1992; Mire-Thibodeaux and Watson
1994). A particular feature of the nematocytes is
that of synthesizing the nematocyst, made up of a
wall and an inverted tubule immersed in the capsule fluid (Mariscal 1974). The application of
chemical and mechanical stimulation (Pantin
1942) results in a rapid extroflexion of the tubule
which penetrates the tissues of the target. injecting toxins of the capsule fluid (Burnett 1991;
Norton 1991; Long and Burnett 1994). This phenomenon is called discharge and it is the most
rapid process of exocytosis known today
(Holstein and Tardent 1984). It is regulated in situ
not only by nematocytes, but also by support and
sensorial cells and, as has recently been shown, a
release of nitric oxide (Salleo et al. 1996); therefore it was deemed as useful to carry out research
on isolated nematocytes in order to eliminate the
possibility of interference by other cells.
So far, either chemical methods, such as
either enzymatic (Anderson and McKay 1987;
McKay and Anderson 1988) or non-enzymatic
(Salleo et al. 1996; Barra et al. 1997), or physical,
such as maceration and heat dissociation
(Schmid et al. 1981; Weber 1995) have been
attempted to isolate nematocytes from various
species. Recently Weber (1995). on the basis of
what Schmid reported (l981). proposed a new
non fixative physical method using two labelling
dyes, in order to investigate nematocyte
turnover and inCUbating Hydra specimens at
40°C for 10 min in a hypertonic medium, obtainIstituto di Fisiologia Generale, Universita di Messina, Salita Sperone 31,98016 Messina, Italy
EM. Faranda, 1.. Guglielmo, G. Spezie (eels)
Mediterranean Ecosystems: Structures and Processes
@ Springer-Verlag ltalia 2001