Final answer:
Sympathetic stimulation enhances excitation-contraction coupling in cardiac muscle by increasing the release of calcium from the sarcoplasmic reticulum, thus increasing the force of muscular contractions.
Step-by-step explanation:
The statement that best describes the effect of sympathetic regulation on Excitation-Contraction (EC) coupling in cardiac muscle is that sympathetic stimulation enhances EC coupling by increasing calcium release from the sarcoplasmic reticulum. This is because the sympathetic nervous system acts as a positive inotrope, meaning it increases the force of contraction of the heart muscle. When sympathetic stimulation occurs, it triggers the release of neurotransmitters like norepinephrine (NE) at the neuromuscular junction from the cardiac nerves and stimulates the secretion of epinephrine and NE from the adrenal cortex. These neurotransmitters bind to alpha and beta receptors on the cardiac muscle cell membrane, leading to an increased metabolic rate and force of contraction. The increase in force is mostly due to the higher amount of calcium ions being released from the sarcoplasmic reticulum, which is essential for the excitation of the muscle and subsequent contraction, as seen in the process of excitation-contraction coupling.