Figure 3.

Behavior of dyspedic cells expressing only CSk3 (a chimeric DHPR) or coexpressing CSk3 and RyR-2. (a) Presence of a large, rapidly activated calcium current in a voltage-clamped dyspedic myotube expressing CSk3. (b) Electrical stimulation (vertical bars) elicited only small, brief Ca²⁺ transients in an intact dyspedic myotube injected only with CSk3 cDNA (top trace). In an intact dyspedic myotube injected with both CSk3 and RyR-2 cDNA (middle trace), electrical stimulation elicited large, long-lasting Ca²⁺ transients (a spontaneous transient occurred between the second and third electrical stimuli). After addition of Cd²⁺ and La³⁺ to block Ca²⁺ current, electrical stimulation failed to evoke transients, although spontaneous transients still occurred (bottom trace, same cell as in middle trace). The cDNA for CSk3 (23) encodes a protein containing amino acids 1–787 and 923-2171 of the cardiac DHP receptor (3) joined by amino acids 666–792 of the skeletal DHP receptor (2).