Minor calyces as primary pacemaker sites for ureteral activity in man.

In isolated preparations of human upper-urinary-tract muscle in the organ-bath, calyceal and subcalyceal areas behave differently. Minor calyx preparations invariably exhibit immediate and extremely regular rhythmical contractions, in direct contrast to preparations of major calyx/pelvis which remain completely quiescent. Specimens of ureter do contract spontaneously but only after periods up to 1 hour. Smooth muscle of the minor calyces possesses excitatory alpha-adrenoceptors, as does that of the remainder of the upper urinary tract; but sensitivity of the minor calyx to alpha-adrenoceptor agonists is far greater than that of preparations from any other site. Furthermore, stimulation of intrinsic nerves can modify activity of the isolated minor calyx, whereas no such effect is observed in any area distal to the minor calyces. These physiological and pharmacological properties of the most proximal areas, considered together with the finding of structurally specialised smooth-muscle cells in this area, form the basis of a hypothesis at that minor calyces in multicalyceal kidneys act as a primary pacemaker sites.