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

Abramcheck, Carla Wilt

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Description

Title

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

Author(s)

Abramcheck, Carla Wilt

Issue Date

1988

Doctoral Committee Chair(s)

Best, Philip M.

Department of Study

Physiology and Biophysics

Discipline

Physiology

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

Biology, Animal Physiology

Abstract

• 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.

Graduation Semester

1988

Type of Resource

text

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