Abstract
We have used the whole-cell clamp technique to investigate inactivation of the ω-conotoxin sensitive high-voltage-activated Ca-channel current (HVA current [2]) carried either by Ca, Ba or Sr (2.5 mM) in chick sensory neurons. At a low internal EGTA concentration (0.1 mM), Ca-channel currents clearly inactivated irrespective of the species of divalent cation carrying the current. During 150 ms pulses, current inactivated to 0.57, 0.67 and 0.75 of the peak current in Ca, Ba and Sr solution, respectively. Time constants of inactivation (26±10 ms and 280±50 ms, mean±S.D., in Ba) were largely independent of the membrane potential. Double-pulse experiments showed that the amount of inactivation left by a pre-pulse was proportional to the amplitude of the current evoked by the pre-pulse. No inactivation was induced by an outward current elicited by a strong depolarization to ü60 mV. With an internal EGTA concentration of 20 mM, the amount of inactivation was significantly smaller. In conclusion, the inactivation of the HVA Ca-channel currents during current flow depends mostly on the entry of divalent cations irrespective of their species.
References
Brehm P, Eckert P (1978) Calcium entry leads to inactivation of calcium channel inParamecium. Science 202:1203–1206
Carbone E, Lux HD (1987) Kinetics and selectivity of a low-voltage-activated calcium current in chick and rat sensory neurones. J Physiol (Lond) 386:547–570
Chad J, Eckert R, Ewald D (1984) Kinetics of calcium-dependent inactivation of caccium current in voltage-clamped neurones of Aplysia. J Physiol (Lond) 347:279–300
Chad J, Eckert R (1986) An enzymatic mechanism for calcium current inactivation in dialysed Helix neurones. J Physiol (Lond) 378:31–51
Dupont JL, Bossu JL, Feltz A (1986): Effect of internal calcium concentration on calcium currents in rat sensory neurons. Pflügers Archiv 406:433–435
Eckert R, Tillotoson DL (1981) Calcium-mediated inactivation of the calcium conductance in caesium-loaded giant neurones ofAplysia Californica. J Physiol (Lond) 314:265–280
Feldman HD, Olivera BM, Yoshikami D (1987) OmegaConus geographus toxin: a peptide that blocks calcium channels. FEBS 214:295–300
Fedulova SA, Kostyuk PG, Veselovsky NS (1985) Two types of calcium channels in the somatic membrane of new-born rat dorsal root ganglion neurones. J Physiol (Lond) 359:431–446
Hadley RW, Hume JR (1987) An intrinsic potential-dependent inactivation mechanism associated with calcium channels in guineapig myocytes. J Physiol (Lond) 389:205–222
Hamill OP, Marty A, Neher E, Sakmann B, Sigworth FJ (1981) Improved patch-clalmp techniques for high-resolution current recording from cells and cell free membrane patches. Pflüger Archiv 391:85–100
Kasai H, Fukuda J, Aosaki T (1987) Presynaptic Ca antagonist ω-conotoxin irreversibly blocks N-type Ca channel current in chick sensory neurons. Neuroscience Research 4:228–235
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Kasai, H., Aosaki, T. Divalent cation dependent inactivation of the high-voltage-activated Ca-channel current in chick sensory neurons. Pflugers Arch. 411, 695–697 (1988). https://doi.org/10.1007/BF00580869
Received:
Revised:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00580869