Isoflurane reduces the carbachol-evoked Ca2+ influx in neuronal cells

Abstract

Background: The authors previously reported that the isoflurane-caused reduction of the carbachol-evoked cytoplasmic Ca2+ transient increase ([Ca2+]cyt) was eliminated by K+ or caffeine-pretreatment. In this study the authors investigated whether the isoflurane-sensitive component of the carbachol-evoked [Ca2+] cyt transient involved Ca2+ influx through the plasma membrane. Methods: Perfused attached human neuroblastoma SH-SY5Y cells were exposed to carbachol (1 mM, 2 min) in the absence and presence of isoflurane (1 mM) and in the absence and presence of extracellular Ca2+ (1.5 mM). The authors studied the effect of the nonspecific cationic channel blocker La3+ (100 μM), of the L-type Ca2+ channel blocker nitrendipine (10 μM), and of the N-type Ca2+ channel blocker ω-conotoxin GVIA (0.1 μM) on isoflurane modulation of the carbachol-evoked [Ca2+]cyt transient. [Ca 2+]cyt was detected with fura-2 and experiments were carried out at 37°C. Results: Isoflurane reduced the peak and area of the carbachol-evoked [Ca2+]cyt transient in the presence but not in the absence of extracellular Ca2+. La3+ had a similar effect as the removal of extracellular Ca2+. ω-Conotoxin GVIA and nitrendipine did not affect the isoflurane sensitivity of the carbachol response although nitrendipine reduced the magnitude of the carbachol response. Conclusions: The current data are consistent with previous observations in that the carbachol-evoked [Ca 2+]cyt transient involves both Ca2+ release from intracellular Ca2+ stores and Ca2+ entry through the plasma membrane. It was found that isoflurane attenuates the carbachol-evoked Ca2+ entry. The isoflurane sensitive Ca2+ entry involves a cationic channel different from the L- or N-type voltage-dependent Ca 2+ channels. These results indicate that isoflurane attenuates the carbachol-evoked [Ca2+]cyt transient at a site at the plasma membrane that is distal to the muscarinic receptor.