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Sparks and Waves in Canine Purkinje Cells A Triple Layered System of Ca 2 Activation

We have investigated the subcellular spontaneous Ca events in canine Purkinje cells using laser scanning confocal microscopy. Three types of Ca transient were found: (1) nonpropagating Ca transients that originate directly under the sarcolemma and lead to (2) small Ca wavelets in a region limited to 6m depth under the sarcolemma causing (3) large Ca waves that travel throughout the cell (CWWs). Immunocytochemical studies revealed 3 layers of Ca channels: (1) channels associated with type 1 IP3 receptors (IP3R1) and type 3 ryanodine receptors (RyR3) are prominent directly under the SL; (2) type 2 ryanodine receptors (RyR2s) are present throughout the cell but virtually absent in a layer between 2 and 4 m below the sarcolemma; (3) type 3 ryanodine receptors (RyR3) is the dominant Ca release channel in the Sub-SL. Simulations of both nonpropagating and propagating transients show that the generators of Ca wavelets differ from those of the CWWs with the threshold of the former being less than that of the latter. Thus, Purkinje cells contain a functional and structural Ca system responsible for the mechanism that translates Ca release occurring directly under the sarcolemma into rapid Ca release in the Sub-SL, which then initiates large-amplitude long lasting Ca releases underlying CWWs. The sequence of spontaneous diastolic Ca transients that starts directly under the sarcolemma and leads to Ca wavelets and CWWs is important because CWWs have been shown to cause nondriven electrical activity. (Circ Res. 2005;97:0-0.)