Late slow outward currents following hyperpolarizing commands are associated with intracellular Ca2+ increase in guinea-pig submucous neurons: investigations with fura-2.
Intracellular recordings were made from submucous neurons in the guinea-pig isolated caecum. A hyperpolarization lasting several seconds followed the termination of a strong hyperpolarizing current pulse; this was always accompanied by a decrease in input resistance. In neurons voltage-clamped at -30 mV, a late slow outward current (LSOC) flowed for more than 10 s, following the termination of a hyperpolarizing command (-100 mV, 2 s). This current was dependent on extracellular K+ concentration, but was not affected by tetraethylammonium, D-tubocurarine and 4-aminopyridine, and was reversibly blocked by low calcium/high magnesium solution. Intracellular calcium concentration ([Ca2+]i) was measured by using a fluorescent calcium indicator, fura-2. In voltage-clamped neurons, [Ca2+]i decreased during the hyperpolarizing command pulse, but increased above the original level at the end of the command. The time course of the change in [Ca2+]i was almost the same as that of the LSOC. Intracellular injection of cesium ions depressed the LSOC, but did not affect the change in [Ca2+]i. The present results indicate that the LSOC is due to activation of calcium-sensitive potassium conductance.
Hirai
K
K
Department of Autonomic Physiology, Tokyo Medical and Dental University, Japan.
Katayama
Y
Y
D000818:Animals; D001572:Benzofurans; D002118:Calcium / Q000502:physiology*; D002432:Cecum / Q000294:innervation*; D004558:Electric Stimulation; D005456:Fluorescent Dyes; D016257:Fura-2; D006168:Guinea Pigs; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials; D011188:Potassium / Q000494:pharmacology; D013368:Submucous Plexus / Q000502:physiology*
D001572:Benzofurans; D005456:Fluorescent Dyes; D008274:Magnesium; D011188:Potassium; D002118:Calcium; D016257:Fura-2