Figure 1.

Schematic of the geometry used in approximate solution of the diffusion equations in the diadic cleft. The diad was treated as two dimensional, and the equations were discretized on a mesh of 10-nm squares (outlined in top left cell). Dihydropyridine receptors were located randomly on mesh squares, whereas ryanodine receptor Ca²⁺ sensing and releasing sites were located on central squares of 3 × 3 blocks; i.e., on a regular square lattice of 30-nm spacing. The approximate positions of the quatrefoil foot processes of the ryanodine receptors are indicated by the tilted squares.