Figure 1.
Scheme of model. A SM cell sarcolemma contains channels, receptors, and transporters shown as rectangles spanning the membrane. Enzymes are represented as circles or octagons. Membrane-bound substrate PIP2 and effector DAG are shown as ovals. A common Ca buffer (BUFFER) is uniformly distributed throughout the cell except in the central SR (SRcen) and the peripheral SR (SRper), in which the Ca buffer is uniformly CSQ. Inorganic ions are shown without their charges and subscripted to indicate their compartment. Subscript “ex” refers to the extracellular milieu, “in” refers to the sarcoplasm, “jun” refers to the junction between the SRper and the sarcolemma, “str” refers to the postulated Ca microdomain around the stretch-activated channel (NSCstr), “cen” refers to the central SR, and “per” refers to the peripheral SR. (The longer subscripts NSCstr, SRper, and SRcen are used in the text and in the program.) The components associated with the junction are highlighted in blue, and those associated with the stretch microdomain are highlighted in orange. Cain, considered uniformly distributed in the sarcoplasm except for the microdomains, is highlighted in black. Other soluble components and effectors are shown in bold lettering. Most components are shown once. The kinases are repeated to be close to their targets, and the inorganic ions are repeated to be close to their sources and sinks. All abbreviations are defined in Materials and methods. A line ending in a closed arrowhead indicates activation; a line ending in a bar indicates inhibition. A closed arrow head pointing at an encircled Vm indicates depolarization, and a barred line indicates hyperpolarization. A line ending in a closed arrow crossed by a bar indicates activation followed by inhibition. A line ending in an open arrowhead indicates a flux between compartments or an enzyme reaction.