Figure 5.

The CGP-sensitive component of the recovery is sensitive to intracellular Na⁺. Depolarization-evoked [Ca²⁺]_i response recorded under voltage clamp (perforated patch conditions). (A) Response to a 2-s depolarization from −70 to −10 mV (pipette solution contained 10 mM Na⁺). After repolarization, the recovery exhibited a prolonged plateau whose magnitude was similar to those seen in intact cells after high K⁺ depolarization. Cell sc0w51. (B) Responses from another Na⁺-containing cell (6.5 mM) elicited first in the presence of 0.8 μM CGP and then 12.5 min after washing out the drug (right) showing reversible suppression of the [Ca²⁺]_i plateau. Inset compares I_Ca elicited by these depolarizations. Cell sc0w42. (C) [Ca²⁺]_i response measured with low intracellular Na⁺. When pipette solutions contained no added Na⁺, the recovery after depolarization lacked a plateau (left) and was not modified by CGP (1 μM, right). In this cell, the second depolarization (-10 mV) was stronger than the first (−15 mV) in an effort to elevate [Ca²⁺]_i to approximately the same level to facilitate comparison of the recoveries. Cell sc0w59. (D) Collected results showing that the [Ca²⁺]_i plateau level observed in cells containing intracellular Na⁺ (6.5–10 mM) is significantly depressed by CGP, that there is no further effect if Na⁺ is omitted from the pipette solution, and that CGP has no detectable effect when intracellular Na⁺ concentration is low (* indicates significant difference from control, P < 0.001).