Cellular Calcium Movements and Excitation-Contraction Coupling in Guinea Pig Atria

86 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1993.Guinea pig left atria were suspended in a tissue bath of normal Krebs-Henseleit solution which was aerated with 95% O$\sb2$/5% CO$\sb2$ and maintained at 27$\sp\circ$C. The atria were attached to a force transducer and impaled with calcium sensitive micro-electrodes. The tissue was stimulated through 2 AgCl electrodes at 2 pulses per second (pps). When the tissue had reached a steady-state of contraction strength, rest intervals of 1 minute were introduced and the changes in the paracellular calcium levels were measured with the calcium sensitive micro-electrodes. The control condition produced an average increase during the interval in paracellular calcium concentration of 23.6 + 1.33 uM. Following treatment of the tissue with 8uM $3\sp\prime, 4\sp\prime$-di-chlorobenzamil (DCB), the average increase in paracellular calcium was 9.02 + 1.25 uM. DCB reduces the normal calcium efflux by 61.6 + 7.3%, n = 4, p $<$ 0.005. (Statistical analysis used paired one tail T-test.) 10 nM Ryanodine treated-tissue showed an increased efflux of calcium as measured by increased para-cellular calcium concentration of 9.8 + 1.9 uM over the control condition. 8uM DCB decreased the ryanodine treated tissues calcium efflux by 53.6 + 8.0%, n = 6, p $<$ 0.005, as measured by a decrease in the paracellular calcium concentration of 10.4 + 1.8 uM compared to the ryanodine treated condition. The cellular calcium efflux may be calculated from the measured changes in paracellular calcium concentration assuming an extracellular space of 47.8 ml/100 gm tissue. 8 uM DCB decreased the calcium efflux by 11.6 nmoles/sec per 100 gm tissue in non-ryanodine treated atria, and by 8.3 nmoles/sec per 100 gm of tissue in ryanodine treated atria. We conclude that DCB is an inhibitor of sodium-calcium exchange in guinea pig atria and that a measurable increase in paracellular calcium occurs during rest due to efflux of calcium from the cells via sodium-calcium exchange. In addition, we have shown that DCB decreases post-rest beat potentiation and this may indicate that sodium-calcium exchange plays a role in post-rest beat potentiation as well as the excitation-contraction coupling process.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD