Question

3) Answer all 3 parts i), ii), and iii).

i) How can you represent a membrane patch in ‘electrical terms’? (2 marks)

ii) Both plant cells and many mammalian nerve cells have relatively low resting chloride (Cl- ) permeabilities. How is it then that plant cells, but not nerve cells, can generate positive-going Cl- -dependent action potentials?

iii) A hormone acts on a mammalian endocrine cell inducing membrane hyperpolarization associated with an increase in membrane conductance. Suggest and explain a plausible ionic mechanism.

Answer 1

i) A small microelectrode is placed close to the membrane. This part of cell membrane is known as patch. That is why the technique is called as patch clamp technique. Then a suction is applied in such a way that a small part of the membrane goes inside the microelectrode. The glass tip of microelectrode forms a seal with the cell membrane. If the amount of suction is increased, then the small part of membrane which is present inside the microelectrode will leave the rest of the membrane. This process occurs in such a way that a seal is formed between the cell membrane and the microelectrode. The electric current can easily be measured during various phases of muscle contraction, relaxation and at rest using this electrode.