Journal of Neurophysiology, Vol 71, Issue 6 2126-2138, Copyright © 1994 by APS

ARTICLES

Characterization of the membrane ion currents of a model molluscan muscle, the accessory radula closer muscle of Aplysia californica. III. Depolarization-activated Ca current

V. Brezina, C. G. Evans and K. R. Weiss
Department of Physiology and Biophysics, Mount Sinai School of Medicine, New York 10029.

1. The accessory radula closer (ARC) muscle of Aplysia californica and its innervation is a model preparation for the study of the neural and cellular mechanisms of behavioral plasticity. Much of the plasticity is due to modulation of contractions of the muscle by a variety of neurotransmitters and peptide cotransmitters. Preliminary to investigating the cellular mechanisms of this modulation, we have characterized the major membrane ion currents present in the unmodulated ARC muscle and their likely roles in normal contraction. We have studied single dissociated but functionally intact ARC muscle fibers under voltage clamp. This is the last of three papers describing this work. In the first paper we characterized two currents prominent at hyperpolarized voltages, a classical inwardly rectifying K current and a Cl current induced by elevated intracellular Cl-. In the second paper we examined two large outward K currents activated at more depolarized voltages, an "A" current and a delayed rectifier. 2. In this paper, we describe an inward depolarization-activated Ca current that underlies and is normally completely masked by the K currents and is revealed when they are blocked. 3. The Ca current begins to activate above -40 or -30 mV. It is fully available for activation at voltages more negative than -60 mV. It activates in milliseconds, then inactivates relatively slowly with maintained depolarization. The current is larger and inactivates slower when it is carried by Ba2+ rather than Ca2+. The inactivation is current rather than voltage dependent. The current is blocked by Co2+, Cd2+, and with a characteristic time dependence, by the dihydropyridine Ca-channel antagonist nifedipine. 4. These properties of the current characterize it as a high-threshold, L-type Ca current. 5. This current most likely provides Ca2+ necessary for contraction of the ARC muscle.

This article has been cited by other articles:

				V. Brezina, I. V. Orekhova, and K. R. Weiss Neuromuscular Modulation in Aplysia. I. Dynamic Model J Neurophysiol, October 1, 2003; 90(4): 2592 - 2612. [Abstract] [Full Text] [PDF]

				I. V. Orekhova, V. Alexeeva, P. J. Church, K. R. Weiss, and V. Brezina Multiple Presynaptic and Postsynaptic Sites of Inhibitory Modulation by Myomodulin at ARC Neuromuscular Junctions of Aplysia J Neurophysiol, March 1, 2003; 89(3): 1488 - 1502. [Abstract] [Full Text] [PDF]

				D. Rokni and B. Hochner Ionic Currents Underlying Fast Action Potentials in the Obliquely Striated Muscle Cells of the Octopus Arm J Neurophysiol, December 1, 2002; 88(6): 3386 - 3397. [Abstract] [Full Text] [PDF]

				M. Jospin, V. Jacquemond, M.-C. Mariol, L. Segalat, and B. Allard The L-type voltage-dependent Ca2+ channel EGL-19 controls body wall muscle function in Caenorhabditis elegans J. Cell Biol., October 28, 2002; 159(2): 337 - 348. [Abstract] [Full Text] [PDF]

				I. V. Orekhova, J. Jing, V. Brezina, R. A. DiCaprio, K. R. Weiss, and E. C. Cropper Sonometric Measurements of Motor-Neuron-Evoked Movements of an Internal Feeding Structure (the Radula) in Aplysia J Neurophysiol, August 1, 2001; 86(2): 1057 - 1061. [Abstract] [Full Text] [PDF]

				S. C. Rosen, M. W. Miller, C. G. Evans, E. C. Cropper, and I. Kupfermann Diverse Synaptic Connections Between Peptidergic Radula Mechanoafferent Neurons and Neurons in the Feeding System of Aplysia J Neurophysiol, March 1, 2000; 83(3): 1605 - 1620. [Abstract] [Full Text] [PDF]

				M. Jeziorski, R. Greenberg, and P. Anderson The molecular biology of invertebrate voltage-gated Ca(2+) channels J. Exp. Biol., January 3, 2000; 203(5): 841 - 856. [Abstract] [PDF]

				M. S. Yeoman and P. R. Benjamin Two Types of Voltage-Gated K+ Currents in Dissociated Heart Ventricular Muscle Cells of the Snail Lymnaea stagnalis J Neurophysiol, November 1, 1999; 82(5): 2415 - 2427. [Abstract] [Full Text] [PDF]

				M. S. Yeoman, B. L. Brezden, and P. R. Benjamin LVA and HVA Ca2+ Currents in Ventricular Muscle Cells of the Lymnaea Heart J Neurophysiol, November 1, 1999; 82(5): 2428 - 2440. [Abstract] [Full Text] [PDF]

				M. L. Scott, V. Brezina, and K. R. Weiss Ion Currents and Mechanisms of Modulation in the Radula Opener Muscles of Aplysia J Neurophysiol, November 1, 1997; 78(5): 2372 - 2387. [Abstract] [Full Text] [PDF]

				J. D. Mills and R. M. Pitman Electrical Properties of a Cockroach Motor Neuron Soma Depend on Different Characteristics of Individual Ca Components J Neurophysiol, November 1, 1997; 78(5): 2455 - 2466. [Abstract] [Full Text] [PDF]

				W. F. Gilly, R. Gillette, and M. McFarlane Fast and Slow Activation Kinetics of Voltage-Gated Sodium Channels in Molluscan Neurons J Neurophysiol, May 1, 1997; 77(5): 2373 - 2384. [Abstract] [Full Text] [PDF]

				P. J. Laurienti and J. E. Blankenship Serotonergic Modulation of a Voltage-Gated Calcium Current in Parapodial Swim Muscle From Aplysia brasiliana J Neurophysiol, March 1, 1997; 77(3): 1496 - 1502. [Abstract] [Full Text] [PDF]