If there are spare β1-adrenergic receptors on cardiac muscle, which statement is correct?

When discussing how spare β1-adrenergic receptors work in cardiac muscle, it's vital to understand the concept of receptor spare or reserve. The presence of spare receptors means that not all receptors need to be occupied to achieve a maximal response to a hormone or neurotransmitter like epinephrine. In the context of cardiac muscle, this indicates that a significant effect can be achieved with only a fraction of the β1-adrenergic receptors being activated.

This principle is particularly important in pharmacology because it highlights how drugs that target these receptors can lead to strong physiological responses, even at lower doses. In this scenario, when only a part of the β1-adrenergic receptors are occupied by epinephrine, the remaining spare receptors can contribute to an amplified effect without requiring full occupancy of all receptors, thus facilitating a maximal response.

Other statements do not align precisely with this principle. For instance, while the number of available β1-adrenergic receptors can influence the biochemical responses to epinephrine, it does not necessarily determine the maximum effect, as that is achieved through the activation of only a portion of the receptors thanks to the reserve capacity of the remaining receptors. Similarly, the existence of spare receptors does not imply reduced sensitivity to ep