Chapter 19, Problem 1P

Summary Introduction

To examine: Whether the statement “given the numerous processes inside cells that are regulated by changes in Ca⁺² concentration, it seems likely that Ca⁺²-dependent cell-cell adhesions are also regulated by changes in Ca⁺² concentration” is true or false.

Introduction:

Cell-cell adhesions play an important role in maintaining the architecture of various tissues. The homophilic and heterophilic adhesion of cells is mediated by many cell-surface proteins (CAMs). CAMs are classified into five categories- cadherins, immunoglobulins, mucins, integrins, and selectins. Out of these, cadherin and selectin based cell adhesions depend on Ca⁺² concentration.

Answer to Problem 1P

Correct answer: The statement is false.

Explanation of Solution

The regulation of various cell-cell interactions and processes are mediated by changes in Ca⁺² concentration through Ca⁺² signaling pathways. Cell surface proteins (CAMs) contribute in cell-cell adhesions. Cadherins come under Ca⁺²-dependent CAMs. The N-terminal extracellular domain is the site for binding of Ca⁺² and thus, adhesion of cells. The removal of Ca⁺² from extracellular medium dissociates the cells causing cadherins to mediate cell-cell adhesion. The cell-cell adhesion is not regulated by Ca⁺² concentration changes as cells cannot control Ca⁺² concentration in their environment. Hence, the statement is false.