Somatostatin activates an inwardly rectifying K+ channel in neonatal rat atrial cells.

Somatostatin, localized throughout the central and peripheral nervous systems, has been found in neurons of the vagal inhibitory pathway of the heart and has been shown to have negative inotopic effects in cardiac tissue. Using patch clamp techniques we show that somatostatin activates an inwardly rectifying K+ channel in rat atrial cells. Loss of somatostatin-induced K+ channel activity in excised inside-out patches is restored by the addition of GTP to the bath. Pertussis toxin pretreatment blocked GTP-dependent somatostatin activation of the inwardly rectifying K+ channel. This K+ channel has a conductance of 34 pS and a mean open time of approximately 1 ms. It is apparently the same K+ channel activated by muscarinic and adenosine receptors in atrial and cardiac pacemaker cells. Thus, atrial cells have at least three receptors which act via pertussis toxin-sensitive G proteins to activate the same class of K+ channels.