A, in the absence of l-NIO, ACh elicited a prominent inhibition of ISO-stimulated ICa,l (-57 %). B, in another atrial myocyte from the same heart, l-NIO attenuated ISO-induced stimulation of ICa,l and enhanced ACh-induced inhibition of ISO-stimulated ICa,l (-78 %). C, summary of the data shows that l-NIO significantly decreased ISO-induced stimulation of ICa,l and significantly enhanced ACh-induced inhibition of ISO-stimulated ICa,l. * P < 0.05.