Ryanodine receptor (RyR) is a calcium release channel protein on the intracellular Ca2+-store. While inositol 1, 4, 5-trisphosphate receptor (IP3R), another intracellular calcium release channel protein, is mainly found in non-muscle cells, such as neurons and hepatocytes, and smooth muscles, RyR is the Ca2+-release channel protein in skeletal and cardiac muscles. At least three genetically distinct isoforms of RyR are identified: isoform proteins Ryrl, Ryr2, and Ryr3 expressed by ryr1, ryr2 and ryr3, respectively. In the central nervous system where IP3R is much more abundant than RyR, the main isoform of RyR is Ryr2, which is specific to the cardiac ventricular muscle. Recently, ryr3 was detected in specific regions of the brain. In this paper, the heterogeneous distribution and localization of RyR isoforms in the brain are summarized. The discussion extends into their putative functions, especially potential involvement in neuronal plasticity.
The mechanism whereby hormones or neurotransmitters activate G proteins and their intracellular effectors can be studied in reconstituted systems using purified components. However, the regulation of receptor-G protein signaling appears to be substantially more complex in the cell and several additional components participate in this event. To study the relationship among G proteins receptors, and effectors in complex systems, such as membranes of permeable cells, it is necessary to employ methods that selectively allow the examination of G protein activation. One such method is photoaffinity labeling using a hydrolysis-resistant, photoaffinity GTP analog, P3 (4-azidoanilido)-P1-guanosine 5'-triphosphate (AAGTP). Here we describe the synthesis and purification of [32P] AAGTP as well as a procedure suitable studying the G protein function in membrane preparations. Photoaffinity labeling in rat cerebral cortex membranes showed that at least four G proteins (GsH, GsL, Gi, and Go) were labeled by [32P] AAGTP. [32P] AAGTP labeling on Gs and Gi was altered in concert with the activation states of those G proteins. An agonistspecific increase in [32P] AAGTP labeling of the G protein α-subunit in a membrane preparation has also been demonstrated. Thus, the photoaffinity labeling method with [32P] AAGTP makes it possible to investigate the behavior of individual G proteins in complex systems such as membrane preparations.