Depolarization of one group of smooth muscle cells rapidly spreads to other smooth muscle cells, leading to coordinated contractions. this electrical coupling is due to
a. autocrine signaling
b. paracrine signaling
c. endocrine signaling
d. direct signaling

The correct answer will be- Direct signalling

Explanation:

Direct signalling is a type of signalling which takes place between the neighbouring cells through gap junctions present between them.

The cardiac muscle cells possess gap junctions which allow the transmission of signals between cells. The cells of the muscle perform the same function simultaneously as the gap junctions allow the transmission of electrical signals.

Since this direct cell to cell transmission of the cell involves the gap junctions and thus direct signalling is the correct answer.

The transfer of signaling molecules communicates the current state of the cell that is directly next to the target cell; this allows a group of cells to coordinate their response to a signal that only one of them may have received. In plants, plasmodesmata are ubiquitous, making the entire plant into a giant communication network.

Gap junctions are particularly important in cardiac muscle: the signal to contract is passed efficiently through gap junctions, allowing the heart muscle cells to contract in unison.

y transferring signaling molecules across gap junctions between neighboring cells.