Single Cell Assays of Excitation‐Secretion Coupling

By adjusting the pattern of stimulation, it is possible to probe the excitation-secretion pathway of an excitable cell with an arbitrary stimulus. Such control over the input combined with the ability to measure simultaneously changes in intracellular [Ca²⁺](i) and increase in cell surface area in a single cell has already produced important new insights into the mechanisms underlying excitation-secretion coupling from an increasing number of laboratories. Although this report has emphasized those features that we find in common in these two neuroendocrine tissues, it should be remembered that in these preparations not all cells are alike. We have not yet made an effort to distinguish cells on the basis of their secreted product. Given that the pattern of electrical activity underlying release in posterior pituitary is different in the oxytocin- and vasopressin- releasing neurons, it is possible that the release process differs in subtle ways that are now beyond our view. Similarly, the cells of the adrenal medulla are divided among those that release epinephrine and those that release norepinephrine. Future work will focus increasingly on the specializations that are necessary for each of these cell types to perform a unique physiological role.