Regulation of a voltage-sensitive release mechanism by Ca-calmodulin-dependent kinase in cardiac myocytes

Zhu, Jiequan, and Gregory R. Ferrier. Regulation of a voltage-sensitive release mechanism by Ca-calmodulin-dependent kinase in cardiac myocytes. Am J Physiol Heart Circ Physiol 279: H2104–H2115, 2000.—A role for Ca-calmodulin-dependent kinase (CamK) in regulation of the voltagesensitive release mechanism (VSRM) was investigated in guinea pig ventricular myocytes. Voltage clamp was used to separate the VSRM from Ca-induced Ca release (CICR). VSRM contractions and Ca transients were absent in cells dialyzed with standard pipette solution but present when 2–5 mM calmodulin was included. Effects of calmodulin were blocked by KN-62 (CamK inhibitor), but not H-89, a protein kinase A (PKA) inhibitor. Ca current and caffeine contractures were not affected by calmodulin. Transient-voltage relations were bell-shaped without calmodulin, but they were sigmoidal and typical of the VSRM with calmodulin. Contractions with calmodulin exhibited inactivation typical of the VSRM. These contractions were inhibited by rapid application of 200 mM of tetracaine, but not 100 mM of Cd, whereas CICR was inhibited by Cd but not tetracaine. In undialyzed myocytes (high-resistance microelectrodes), KN-62 or H-89 each reduced amplitudes of VSRM contractions by ;50%, but together they decreased VSRM contractions by 93%. Thus VSRM is facilitated by CamK or PKA, and both pathways regulate the VSRM in undialyzed cells.