Key result
Adenosine 5' triphosphate and muscarine suppressed steady-state M-conductance in bullfrog sympathetic B-neurones without decreasing activation or deactivation time constants.
The findings cast doubt on the hypothesis that elevation of intracellular Ca2+ is involved in the transduction mechanism for ATP- or muscarine-induced M-conductance suppression in bullfrog sympathetic B-neurones.
Questions Ca2+ role in M-conductance suppression by ATP and muscarine; leaves open applicability to mammalian sympathetic neurons.
Adenosine 5' triphosphate (ATP) (0.5-500 microM) or muscarine (0.1-1.0 microM) suppressed M-current/conductance (IM/gM) in B-cells of bullfrog sympathetic ganglion. Both agonists suppressed steady-state M-conductance (gM) at -30 mV and there was either no change or a slight increase in the time constants for gM activation (tau(a) at -30 mV) and deactivation (tau(d) at -50 mV). 2. It has previously been shown that experimental elevation of intracellular Ca2+ concentration ([Ca2+]i) suppresses gM and this is associated with decreases in both tau(a) and tau(d). As these changes in kinetics differ from those we observe with agonist application, our results cast doubt on the hypothesis that elevation of [Ca2+]i is involved in the transduction mechanism for ATP- or muscarine-induced gM suppression.
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Chen et al. (2001) studied this question. Adenosine 5' triphosphate (ATP) or muscarine was evaluated on M-current/conductance (IM/gM) suppression and time constants for gM activation and deactivation. Adenosine 5' triphosphate and muscarine suppressed steady-state M-conductance in bullfrog sympathetic B-neurones without decreasing activation or deactivation time constants.
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