In Vitro Characterization of L-Type Calcium Channels and Their Contribution to Firing Behavior in Invertebrate Respiratory Neurons

1 Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada; and 2 Department of Molecular and Cellular Neurobiology, Research Institute Neurosciences, Vrije Universiteit, Amsterdam, The Netherlands Submitted 24 June 2005; accepted in final form 7 September 2005 L-type calcium channel activity has been associated with a number of cytoplasmic responses, including gene transcription and activation of calcium-dependent enzymes, yet their direct contribution to the electrical activities of neurons has remained largely unexplored. Here we report the cloning and functional characterization of a molluscan L-type calcium channel homologue, LCa v 1 , and investigate its role in coordinating neuronal firing patterns. The LCav1 channel exhibits many hallmarks of vertebrate L-type channels in that it is high-voltage activated, slowly inactivating, and dihydropyridine sensitive and displays calcium-dependent inactivation in recording solutions with standard EGTA concentrations. We show that despite comprising less than 20% of the total whole cell current in identified Lymnaea respiratory network neurons, the L-type channels are essential for maintaining rhythmic action potential discharges without being involved in synaptic release. Our data therefore suggest an important role of L-type calcium channels in maintaining rhythmical pattern activity underlying breathing behavior in Lymnaea . Address for reprint requests and other correspondence: G. W. Zamponi, Dept. of Physiology and Biophysics, 3330 Hospital Dr. NW, Calgary, T2N 4N1, Canada (E-mail. Zamponi{at}ucalgary.ca )