Question

Consider a hypothetical cell whose plasma membrane is impermeant to everything. The membrane is studded with channel proteins for Ca2+, but these channels are initially closed. The concentration of Ca2+ outside the cell is 100 mM and the concentration of Ca2+ inside the cell is 1 mM. Initally, the membrane potential is 0 mV.

a) In response to a signal molecule, all of the Ca2+ channel proteins suddenly become open. In which direction is there a net flow of Ca2+? Why?

Answer 1

a).

Given that the hypothetical cell was not permeable to anything, and the membrane potential is 0 mV initially. A resting membrane potential is negative.

In the given case, the calcium concentration outside the cell is, 100 mM (milli moles), whereas the intracellular calcium concentration is, 1 mM. So, assuming that a resting membrane potential is negative, the calcium moves from inside to the outside in order to attain a negative membrane potential (as the calcium ions are positively charged).