An 88-Year-Old Nursing Home Resident Has Diabetes Mellitus and Is

An 88-year-old nursing home resident has diabetes mellitus and is taking diuretics for hypertension. His blood glucose concentration has recently been greater than 350 mg/dL. He is disoriented and has had limited oral intake for about 5 days. His vital signs include a temperature of 100.5°F, a supine blood pressure of 150/90 mm Hg and pulse of 100 beats/min, and an upright blood pressure of 130/88 mm Hg and pulse of 118 beats/min. The findings on examination of the heart are normal, and his axillae are dry. The table shows serum Na⁺ and K⁺ values before and after the dehydration that has occurred in this patient. The resting membrane potential of a cardiac myocyte was about ?70 millivolts before dehydration occurred. What is the resting membrane potential of a cardiac myocyte after dehydration occurred, assuming no change in membrane conductance or intracellular concentrations of Na⁺ or K⁺? $$\begin{array} { | l l c | } \hline & \underline { \text { Before } } & \underline { \text { After } } \\\mathrm { Serum } ^ { \mathrm { Na } } { } ^ { + } & 140 \mathrm { mmol } / \mathrm { L } & 151 \mathrm { mmol } / \mathrm { L } \\\text { Serum } \mathrm { K } ^ { + } & 3.5 \mathrm { mmol } / \mathrm { L } & 3.5 \mathrm { mmol } / \mathrm { L } \\\hline\end{array}$$

A) -100 millivolts
B) -50 millivolts
C) -60 millivolts
D) -70 millivolts
E) -90 millivolts