Interplay Among Distinct Ca2+ Conductances Drives Ca2+ Sparks/Spontaneous Transient Outward Currents In Rat Cerebral Arteries

Ca2+ sparks are generated in a voltage-dependent manner to initiate spontaneous transient outward currents (STOCs), events that moderate arterial constriction. In this study, we defined the mechanisms by which membrane depolarization increases Ca2+ sparks and subsequent STOC production. Using perforated patch clamp electrophysiology and rat cerebral arterial myocytes, we monitored STOCs in the presence and absence of agents that modulate Ca2+ entry. Beginning with Ca(V)3.2 channel inhibition, Ni2+ was shown to decrease STOC frequency in cells held at hyperpolarized (-40mV) but not depolarized (-20mV) voltages. In contrast, nifedipine, a Ca(V)1.2 inhibitor, markedly suppressed STOC frequency at -20mV but not -40mV. These findings aligned with the voltage-dependent profiles of L- and T-type Ca2+ channels. Furthermore, computational and experimental observations illustrated that Ca2+ spark production is intimately tied to the activity of both conductances. Intriguingly, this study observed residual STOC production at depolarized voltages that was independent of Ca(V)1.2 and Ca(V)3.2. This residual component was insensitive to TRPV4 channel modulation and was abolished by Na+/Ca2+ exchanger blockade. In summary, our work highlights that the voltage-dependent triggering of Ca2+ sparks/STOCs is not tied to a single conductance but rather reflects an interplay among multiple Ca2+ permeable pores with distinct electrophysiological properties. This integrated orchestration enables smooth muscle to grade Ca2+ spark/STOC production and thus precisely tune negative electrical feedback.