. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 138 C. D. McCAIG. Figure 2. (a) Control nerve. Scale bar = 25 urn. (b) Same nerve after 84 min exposure to Co*4 (5 mAf), A23187(10 jiM) and HOmV/mm. Nerve has oriented towards the anode at right, (c) Fluorescence micro- graph of neuronal cell body after 1 h exposure to Co++ (5 mAO, A23187 (15 MA/), and 100 mV/mm and fixed in culture medium + 4% formal- dehyde. Under UV excitation A23I87 is fluorescent and is localized predominantly on the anodal-facing side of cells (right). Cells fixed but not exposed to A23187 showed no au
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 138 C. D. McCAIG. Figure 2. (a) Control nerve. Scale bar = 25 urn. (b) Same nerve after 84 min exposure to Co*4 (5 mAf), A23187(10 jiM) and HOmV/mm. Nerve has oriented towards the anode at right, (c) Fluorescence micro- graph of neuronal cell body after 1 h exposure to Co++ (5 mAO, A23187 (15 MA/), and 100 mV/mm and fixed in culture medium + 4% formal- dehyde. Under UV excitation A23I87 is fluorescent and is localized predominantly on the anodal-facing side of cells (right). Cells fixed but not exposed to A23187 showed no autofluorescence. present throughout the ensuing 16 h. Interestingly, the rate of nerve growth almost doubled during the first 2 h in the field, and 88% of nerves turned towards the cath- ode (35/40; Table 1). Therefore, procedures that may re- verse the field-induced asymmetry of the con A receptors did not influence galvanotropism. A role for Ca++ in galvanotropism'.' Elongating neurites were exposed to the calcium chan- nel blocker Co++ (5 roA/) and simultaneously to an ap- plied electric field. Co+ + significantly slowed nerve ad- vance, although slow rates of growth were maintained over a 12-h period. Around 80% of processes showed no orientation to the electric field (23/29). An intriguing method for reversing the galvanotaxis offish keratocytes similarly points to a role for calcium (Cooper and Schliwa, 1986) and has been applied to Xen- opus neurites. Orientation was inhibited in the presence of Co++. The calcium ionophore A23187 did not affect orientation; 11/12 nerves turned towards the cathode. When these procedures were combined (, 5 mMCo++ plus 15 nM A23187 plus 100 mV/mm), 62% of nerves showed reversed galvanotropism and turned towards the anode (13/21). Examination of neuronal somata under UV excitation revealed that fluorescence from the iono- phore was predominant in the anodal-facing half of cells (Fig. 2; Table I). Discussion Nerves orient to a variety of e
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