Co-expression of ryanodine receptor type3 and Ca2+ activated K+ channels in HEK293 cells

Type 3 ryanodine receptor (RyR3) is widely expressed in various tissues but its functional roles have not been fully understood. In some organs, it is considered that Ca2+ oscillations generate pacemaker potentials via stimulation of Ca2+-activated ion channels, such as Ca2+-activated K+ channel (Kr). To examine the functional roles of RyR3 in the regulation of Ca2+-dependent ion channels, RyR3 was transiently expressed in HEK293 cells (HEK-RyR3) where Ca2+ activated K+ channels (KCa), Small-conductance KCa (SK) or Large-conductance KCa (BK), were stably expressed. The expression of RyR3 per se showed spontaneous Ca2+ oscillations (averaged frequency: 1. 3 mm-1). Co-expression of RyR3 with BK or SK channels did not change the averaged frequency of Ca2+ oscillation; 1. 2 and 1. 4 mm-1, respectively. Membrane potentials, together with [Ca2+]i, were measured using perforated patch clamp techniques. The rise of [Ca2+]i caused concomitant membrane hyperpolarization, which propagated to adjoining cells where KCa were expressed but RyR3 were not. This re-constituted system may be a useful model to analyze the contribution of RyR3 to pacemaker potential generation via activation of KCa