Increased intracellular Na+ causing increased efflux of Na+ and increased infl ux of Ca++ through Na+/Ca++ exchanger in the sarcolemma.

Decreased efflux of Na+ leading to less negative resting membrane potential and opening of voltage gated Ca++ channels on the T tubules.

Decreased activity of Na+/Ca++ exchanger causing decreased influx of sodium and decreased efflux of Ca++ in the sarcolemma.

Increased intracellular Na+ decreasing the activity of Ca++ pump in the sarcoplasmic reticulum.