Published online before print June 9, 2005, doi: 10.1161/01.RES.0000173375.26489.fe
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Submitted on August 10, 2004
Revised on May 9, 2005
Accepted on June 1, 2005
Ca2+ Sparks and Waves in Canine Purkinje Cells. A Triple Layered System of Ca2+ Activation
Bruno D. Stuyvers *;
From the Departments of Medicine (B.D.S., H.E.D.J.t.K.), Physiology, and Biophysics, University of Calgary, Alberta, Canada; the Departments of Pharmacology (W.D., P.A.B., H.E.D.J.t.K.) and Molecular Cardiology (S.M.), Center for Molecular Therapeutics, Columbia University, New York; and the Department of Neuroscience (V.S.), University of Siena, Italy.
* To whom correspondence should be addressed. E-mail: stuyvers{at}ucalgary.ca.
We have investigated the subcellular spontaneous Ca2+ events in canine Purkinje cells using laser scanning confocal microscopy. Three types of Ca2+ transient were found: (1) nonpropagating Ca2+ transients that originate directly under the sarcolemma and lead to (2) small Ca2+ wavelets in a region limited to 
6-µm depth under the sarcolemma causing (3) large Ca2+ waves that travel throughout the cell (CWWs). Immunocytochemical studies revealed 3 layers of Ca2+ 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 µm below the sarcolemma; (3) type 3 ryanodine receptors (RyR3) is the dominant Ca2+ release channel in the Sub-SL. Simulations of both nonpropagating and propagating transients show that the generators of Ca2+ 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 Ca2+ system responsible for the mechanism that translates Ca2+ release occurring directly under the sarcolemma into rapid Ca2+ release in the Sub-SL, which then initiates large-amplitude long lasting Ca2+ releases underlying CWWs. The sequence of spontaneous diastolic Ca2+ transients that starts directly under the sarcolemma and leads to Ca2+ wavelets and CWWs is important because CWWs have been shown to cause nondriven electrical activity.
Key words: Purkinje • Ca2+ sparks • Ca2+ waves • Ca transients • automaticity
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