Characteristics of cytosolic Ca2+ elevation induced by muscarinic receptor activation in single adrenal chromaffin cells of the guinea pig.
In Fura-2 loaded-single guinea pig adrenal chromaffin cells, muscarine, nicotine and KCl all caused an early peak rise in intracellular Ca concentration ([Ca2+]i) followed by a sustained rise. In Ca(2+)-free solution, muscarine, but neither nicotine nor KCl, caused a transient increase in [Ca2+]i, which was partially reduced by preceding application of caffeine or by treatment with ryanodine plus caffeine. In voltage-clamped cells at a holding potential of -60 mV, the muscarine-induced [Ca2+]i rise, especially its sustained phase, decreased in magnitude. Intracellular application of inositol 1,4,5-trisphosphate caused a transient increase in [Ca2+]i and inhibited the following [Ca2+]i response to muscarine without affecting responses to nicotine and a depolarizing pulse. Muscarine evoked membrane depolarization following brief hyperpolarization in most cells tested. There was a significant positive correlation between the amplitude of the depolarization and the magnitude of the sustained rise in [Ca2+]i. Muscarine-induced sustained [Ca2+]i rise was much greater in the current-clamp mode than that in the voltage-clamp mode. The sustained phase of [Ca2+]i rise and Mn2+ influx in response to muscarine were suppressed by a voltage-dependent Ca2+ channel blocker, methoxyverapamil. These results suggest that stimulation of muscarinic receptors causes not only extracellular Ca2+ entry, but also Ca2+ mobilization from inositol 1,4,5-trisphosphate-sensitive intracellular stores. Voltage-dependent Ca(2+)-channels may function as one of the Ca2+ entry pathways activated by muscarinic receptor in guinea pig adrenal chromaffin cells.
Laboratory of Pharmacology, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, Japan. tohta@vetmed.hokudai.ac.jp
T
T
Ohta
T
T
Asano
S
S
Ito
N
N
Kitamura
Y
Y
Nakazato
D000311:Adrenal Glands / Q000378:metabolism*; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000378:metabolism*; D006168:Guinea Pigs; D018721:Muscarinic Agonists / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011976:Receptors, Muscarinic / Q000378:metabolism*; D012433:Ryanodine / Q000494:pharmacology; D015398:Signal Transduction
D015220:Calcium Channels; D018721:Muscarinic Agonists; D011976:Receptors, Muscarinic; D012433:Ryanodine; D002110:Caffeine; D002118:Calcium