Clustering Of Insp_3 Receptors By Lnsp_3 Retunes Their Regulation By Lnsp_3 And Ca~(2+)

摘要

The versatility of Ca~(2+) signals derives from their spatio-temporal organization1'2. For Ca~(2+) signals initiated by inositol-l,4,5-tris-phosphate (InsP_3), this requires local interactions between InsP_3 receptors (InsP_3Rs)4 mediated by their rapid stimulation and slower inhibition4 by cytosolic Ca~(2+). This allows hierarchical recruitment of Ca~(2+) release events as the InsP_3 concentration increases. Single InsP_3Rs respond first, then clustered InsP_3Rs open together giving a local 'Ca~(2+) puff, and as puffs become more frequent they ignite regenerative Ca~(2+) waves1'5"9. Using nuclear patch-clamp recording10, here we demonstrate that InsP_3Rs are initially randomly distributed with an estimated separation of ～1 μm. Low concentrations of InsP_3 cause InsP_3Rs to aggregate rapidly and reversibly into small clusters of about four closely associated InsP_3Rs. At resting cytosolic [Ca~(2+)], clustered InsP_3Rs open independently, but with lower open probability, shorter open time, and less InsP_3 sensitivity than lone InsP_3Rs. Increasing cytosolic [Ca~(2+)] reverses the inhibition caused by clustering, InsP_3R gating becomes coupled, and the duration of multiple openings is prolonged. Clustering both exposes InsP_3Rs to local Ca~(2+) rises and increases the effects of Ca~(2+). Dynamic regulation of clustering by InsP_3 retunes InsP_3R sensitivity to InsP_3 and Ca~(2+), facilitating hierarchical recruitment of the elementary events that underlie all InsP_3-evoked Ca~(2+) signals.