Vol. 134, No. 3, 1986 BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS February 13, 1986 Pages 1245-1253 C-KINASE ACTIVATION PROLONGS Ca 2+-DEPENDENT INACTIVATION OF K+ CURRENTS Daniel L. Alkon,+ Michinori Kubota, Joseph T. Neary, Shigetaka Naito, Douglas Coulter, and Howard Rasmussen* Section on Neural Systems, Laboratory of Biophysics, National Institute of Neurological and Comnunicative Disorders and Stroke, National Institutes of Health at the Marine Biological Laboratory, Woods Hole, MA 02543 *Departments of Cell Biology and Internal Medicine, Yale University School of Medicine New Haven, CT 06510 Received January 2, 1986 SUMMARY: Voltage-dependent Kt currents, IA and ICaZ+-Kt, across the soma membrane of the Hermissenda Type B photoreceptor, have been shown to remain reduced during retention of classically conditioned behavior. IA and ICaZ+-Kt undergo prolonged reduction due to CCa2+1i elevation produced by a sinj+le pairing of a light step with a command depolarization or by iontophoretic injection of Ca . of transient Ca2+ Onepathway which could contribute to the conversion -mediated reduction of K currents to the persistent reduction observed with conditioning is that involving C-kinase. To examine the role of C-kinase in the long-term regulation of Kt currents, isolated Type B somata were exposed to at least 25- 30 minutes' incubation in artificial sea water (ASW) containing the C-kinase activators 1-oleoyl-2-acetyl-glycerol (OAG) or 12-deoxyphorbol 13-isobutyrate ZO-acetate (DPBA) or control substances [e.g., distearyolglycerol (DiSGII. After exposure to activator (but not to control solutions) and voltage-clamp conditions which caused elevation of cytosolic Ca2+, reductions of IA and ICa2+-Kt were observed which did not reverse (up to 3 hr),even after the activator was removed. Without conditions which induced elevation of cytosolic calcium prolonged incubation with the C-kinase activators had no effect on the membrane currents. Similar exposure of homogenates of the Hermissenda nervous system to OAG and Ca2+ caused enhanced phosphorylation of specific proteins, indicating the presence of C- kinase in the Hermissenda nervous system. @I 1986 Academic Press, Inc. A major question concerning the role of calcium in regulating relatively long-term physiological responses to extracellular stimuli centers on the transient nature of the calcium signal. In response to stimuli such as hormones, neurotransmitters, and depolarization, cytosolic Cazt, CCaztlc, rises quickly, but in many systems it then +To whom correspondence should be addressed. Abbreviations used: ASW, artificial sea water; CaM, calmodulin; [Caztlc, Caztconcentra- tion in cytosol; C-kinase, Cazt -activated/phospholipid-dependent protein kinase; CNS, circumesophageal nervous system; DG, diacylglycerol; DiSG, 1,2 distearoyl-rat-glycerol; DPBA,lZ-deoxyphorbol-13-isobutyrate-ZO- cetate; DIT? dithiothreitol; EGTA, ethylene 19 glycol-bis-(B-aminoethyl ether)-N,N,N ,N outward potassium current; ICa2+-Kt, ,-tetraacetic acid; IA, early voltage-dependent calcium-dependent outward potassium current; PS, phosphatidylserine; OAG, 1-oleoyl-2-acetyl-glycerol; NaDodSO4, sodium dodecyl sulfate. 0006-291X/86 $1.50 1245 Copyright 0 1986 by Academic Press, Inc. All rights of reproduction in any form reserved.