Activation of chloride current by purinergic stimulation in guinea pig heart cells.

Single atrial cells from guinea pig heart were voltage-clamped using the whole-cell configuration of the patch-clamp technique under conditions in which most of the ionic and exchange currents known in cardiac cells were minimized. Extracellular 5 or 50 microM ATP activated a Cl- current, in addition to a rapidly desensitizing cation-selective current. A nonhydrolyzable ATP analogue, adenosine-5'-O-(3-thiotriphosphate) (50 microM), also evoked these two currents, indicating involvement of purinoceptors rather than ecto-ATPase on the membrane. ADP, AMP, and adenosine were also effective in inducing the Cl- current, showing no clear order of potency for the purinoceptor subtypes involved. The purinoceptor-activated Cl- current, like the beta-catecholamine-cAMP-dependent cardiac Cl- current, showed outward rectification and time independence.