[Effects of nitrous oxide and isoflurane on the L-type calcium current of rabbit ventricular myocytes and their modulation by beta-adrenoceptor stimulation].

Background: We compared the effects of nitrous oxide (N2O) plus isoflurane with equianesthetic isoflurane alone on the L-type calcium current (I(Ca,L)), and also investigated their modulation of beta-adrenoceptor stimulation.

Methods: I(Ca,L) was recorded from enzymatically isolated rabbit ventricular myocytes using the whole-cell patch clamp technique. Ventricular myocytes were exposed to prepluses of -40 mV from a holding potential of -80 mV and then to +50 mV in 10 mV increments and thereafter the depolarization pulses that acquire peak currents were applied every 10 seconds. The changes in I(Ca,L) were measured in exposure to experimental gases of 1 MAC:1) 0.5% isoflurane and N2O:O2 (2:1) (I-N20) and 2) 1.15% isoflurane and N2:O2,(2:1) (I-N2).

Results: I-N2O and I-N2 depressed the peak I(Ca,L) by 15.6 +/- 9.2 and 14.6 +/- 8.1%, respectively. In the presence of 1 microM isoproterenol or 10 microM forskolin, the depression by I-N20 was significantly suppressed, but not by I-N2.

Conclusions: The results show that I-N2O and I-N2 depressed I(Ca,L) to a similar degree without beta-adrenoceptor stimulation. The depression by I-N2O, however, was modulated by beta-adrenoceptor stimulation. Beta-adrenoceptor stimulation was thus found to modulate the effect of N2O combined with isoflurane rather than equianesthetic isoflurane alone.