The Role of Potassium as a Counterion During Calcium Release From the Sarcoplasmic Reticulum

100 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988.There is great interest in the effect of Ca$\sp{2+}$ release on the electrical properties of the sarcoplasmic reticulum (SR) membranes since a voltage change may play an important role in muscle regulation. Hence the role of K$\sp{+}$ as a counterion during Ca$\sp{2+}$ release from the SR was investigated and found to be physiologically important.The resting K$\sp{+}$ permeability of the SR membrane was determined from the passive efflux of $\sp{42}$K from single skinned skeletal muscle fibers. The efflux curves were kinetically complex and were fit as the sum of three exponentials. In experiments using pretreatment with detergent or $\sp $C-sucrose the efflux curve lacked the intermediate component. Therefore we concluded that the intermediate component represented movement across a membrane-bound space with a relative fiber volume equivalent to that of the SR. Our estimate of the in situ K$\sp{+}$ permeability for the SR based on the efflux data is 10$\sp{-7}$ cm/sec and is sufficient to support a large K$\sp{+}$ counterion flux.The effect of a decreased SR K$\sp{+}$ conductance on the early Ca$\sp{2+}$ release rate was investigated. An optical technique using the Ca$\sp{2+}$-sensitive dye Antipyrylazo III was used to monitor caffeine stimulated Ca$\sp{2+}$ release from skinned skeletal muscle fibers. The SR K$\sp{+}$ channel blocker bisG10 and substitution of the impermeant ion choline for K$\sp{+}$ were used as two different methods to decrease SR K$\sp{+}$ conductance. Both methods caused a concentration dependent decrease in the Ca$\sp{2+}$ release rate. Therefore we concluded that K$\sp{+}$ is a counterion for Ca$\sp{2+}$ during its release from the SR.The optical technique was then used to determine the selectivity sequence of the in situ SR K$\sp{+}$ channel to several monovalent cations by substituting them for K$\sp{+}$. These ions will effect Ca$\sp{+}$ release dependent on their ability to support counterion flux which is a function of their relative conductance to the SR K$\sp{+}$ channel. The selectivity sequence determined by these experiments was: K$\sp{+}$ = Rb$\sp{+}$ = Na$\sp{+}$ $>$ Cs$\sp{+}$ $>$ Li$\sp{+}$ $>$ choline.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD