Acta Biologica 46. (1995)
2-4. szám - L. Erdélyi: Na+ and Ca2+ cooperatively down regulate the A-type potassium currents in Helix neurons
Acta Biologica Hungarica 46 (2—4), pp. 417—425 (1995) Na+ AND Ca2+ COOPERATIVELY DOWN REGULATE THE A-TYPE POTASSIUM CURRENTS IN HELIX NEURONS* L. ERDÉLYI Department of Comparative Physiology, Attila József University, Szeged, Hungary (Received: 1995-07-31) Modulatory actions of Na+, Tris+, Li+ and Ca2+ on A-type potassium currents were investigated in identified neurons of the snail, Helix pomatia L. А-currents were isolated under spike threshold voltages by use of the double pulse method in combination with computer techniques. To estimate the action of Na+ on A-type potassium currents the normal physiological solution was changed to Na-free (mannitol) medium which increased the amplitude of the А-currents at -30 mV membrane potential by 20.5% without significant modulation of the time-dependent inactivation. When Tris-HCl or LiCl substituted for NaCI, the amplitude of the А-currents decreased by 27.5 or 32.5%, respectively. Li+ did not modify the time constant of decay of the А-currents, but Tris+ decreased it by 15.8%. There was an increase of the amplitude of the А-currents in the Na-, Ca-free (Tris) medium relative to the Na-free (Tris) solution by 27.7% and a decrease of the time constant of decay by 25.3%. It is concluded that А-currents are down regulated by Na+ and Ca2+ under physiological cicrcumstances, but the modulatory action of Ca2+ is more complex and influences the amplitude, time-dependent inactivation and potential-dependent inactivation characteristics of 1д. Among monovalent cations, the А-current attenuation increases in the sequence of Na+ X,Tris+ <Li+. All identified neurons react in a similar way but with different sensitivities. Keywords: Helix neurons — A-type current — ionic modulation — voltage clamp ^Presented at the 8th ISIN Symposium "Neurobiology of Invertebrates", Dune 27—July 2, 1995, Tihany, Hungary Send offprint requests to. Dr. L. Erdélyi, Department of Comparative Physiology, P.D. Box 533, H-6701 Szeged, Hungary 0236-5383/95/# 5.00 © 1995 Akadémiai Kiadó, Budapest