Figure 8.

Effects of cyclic nucleotides (db-cAMP and 8-Br-cGMP) on the voltage-dependent activation and inactivation of I_Ba in guinea-pig antrum. Whole-cell recording, pipette solution Cs⁺-TEA⁺ solution containing 5 mM EGTA and the bath solution 10 mM Ba²⁺ containing 135 mM TEA⁺. Steady-state inactivation curves, obtained in the absence (control) and presence of cyclic nucleotides, were fitted to the Boltzmann equation. Peak current values were used. The steady-state inactivation curve was obtained using the double-pulse protocol (see Methods). The current measured during the test pulse is plotted against membrane potential and expressed as relative amplitude. Activation curves were obtained from the current–voltage relationships, fitting to the Boltzmann equation (see Methods). (a) The steady-state inactivation curves in the absence or presence of db-cAMP (1 mM) were drawn using the following values: (control), I_max=1.0, V_half=−38, k=7.0 and C=0.04; (db-cAMP, 1 mM), I_max=1.0, V_half=−39, k=7.0 and C=0.04. Each symbol indicates the mean of six observations with±s.d. shown by vertical lines. Some of the s.d. bars are less than the size of the symbol. (b) The steady-state inactivation curves in the absence or presence of 8-Br-cGMP (1 mM) were drawn using the following values: (control), I_max=1.0, V_half=−36, k=8.0 and C=0.06; (8-Br-cGMP, 1 mM), I_max=1.0, V_half=−37, k=7.8 and C=0.06. Each symbol indicates the mean of six observations with±s.d. shown by vertical lines. Some of the s.d. bars are less than the size of the symbol.